Resinous composition method of coating metals therewith to increase hightemperature resistance thereof and article produced thereby



Jan. 11, 1955 MARTENS ET AL 2,699,407

RESINOUS COMPOSITION METHOD OF COATING METALS THEIREWITH TO INCREASE HIGH-TEMPERATURE RESISTANCE THEREOF AND ARTICLE PRODUCED THEIREBY Filed Aug. 26, 1952 INVENTURS BY Msa Patented Jan. 11,1955

RESINOUS COMPOSITION METHOD OF COATIN G METALSI THEREWITHJ T05 INCREASE" HIGH- TEMPERATURE RESISTANCE THEREOF AND ARTIGLE PRODUCED THER'EBY Charles RMartensQPairma Heights, and J ohniG Bellamy, In, ,Gleveland; Ohio assign'orstto The Sherwin-Williams- Company; (Eleveland,uhio;ia corporation of Ohio Application-Aug.26,1952, Serial'No. 306574 6 Cli 1itns. (Cli 1 17- -65) This invention relates as indicated to a new anduseful methodfor improvingthe resistance of metal tojextremely, high temperatures" and particularly such temperatureswhich are sufiicientfto cause the? metal to. fuse. More particularly, this invention isdirectetl'to the method of producinganexpendable or one shot article which article is to be subjected for' short periods of? time to temperaturesgenerally well in excess of the melting point of'the metalfrom whicltthe article is manufactured.

Expendable or one short devices are rapidly assumingi arole of ever-increasing importance, particular.- ly from amilitaty standpoint, and especially in the field of rockets" and jet assisted take-oil tubes. Normally, devices such as these are used only once, no attempt being made to recover the shelllor casing after the initial firing. In many cases the cost of the device and the weight ofthe" device are'-- important factors. particularly where aircraft arejinvolved. It has been found desirable toj' construct such devices from light metals such as. aluminum, magnes um, various alloys of aluminum and magnesium," and'in" other cases ou'tof the usualheavy metals but Whereth'e' thicknessbf'the metal is so reduced as remake them: much lighter in Weight.

This 'atttfempt at reduction of 'tlre'weight of such" devices. has'largelymet with failure. because of the fact thatthe metals sought to be'erhployedfleither' hadtoo low a melting point to withstand the temperatures of the, explosive or propulsive charges, orthemetahwas too thintowith stand the temperatures employe'd'for a period of time sutficient: for. theexplosive: or propulsive charge to 'b'ef comeiexpendedl Manyrattempts tovsolve" tliisrproble'm by, coating the metalr a rticle withi various-plastic com positions: have: met with: failure.

It' is a'hprimaryl object? ofwthis invention; therefore; to. provide a method for: improving the: resistance of metals to-"te'mperaturesr sufficient :tor soften .the metali' whereby a life of the article 1 involved isobtained such. that an" ex plosive or propulsive wcharge may; be expended? entirely before: disintegration -of .th'e metala'occurs.

Another object ofthis inventiorivisl-toprovidl arliquid' a coating composition which is suitable for use as a coating for metals which are'to be subjected to temperatures generally in excess of the softeningxpoint of the metal? Another object ofi this: inventionl is to provider a C011? venient and inexpensive method for prolonging the time: during which a metal i may be exposed: to temperatures in excess of the meltingtpoint of such metal:

Other objects Oh this. invention will appear as the: description proceeds.

Tothe accomplishment of the foregoing and related ends, said: invention, then, consists. of the means: heree inafter fully described and particularly pointednout: in the appended claims; the following,- description at setting forth indetail certain illustrativeembodiments of the invention, such disclosedmeans constituting;.howevel1. but a few of the various-forms in. which the principle of' this; invention may be emplbyed.

In the adaptations: of: this: invention which; are of:

primary importance the increased time. of resistance to' of the:

temperatures in excess: of melting, point metal. need'only be a matter of afewseconds; ltwill be understood,qofucourse, that increasing-thickness of the: metal itselfr will improve? the time" during; which the' article can withstand temperatures in excess; of; the? melt? ing point? provided; however; that' thoseu temperatures a are not .soi greatlyrinlexcess ofi the melting point at reason ablenthicknesses and variations thereofi. play a minor role in thelservir'ce life: of the article. i It is possible, therefore, to obtaint correlatable and. indicative results by testing the cffectiveness ofi this inventioniwith panels' ot' various metalsssuch as aluminum; magnesium, alloys of aluminum andi magn'esium; ilOIl;Sll6l, and various other alloys ofirom Tiniandstinwplated articles may also be protected in? accordance with this inventionn An interestingexampleof .til'lfifil'llbOdll'IlBl'llOfw[hiSdflVenfiOH may be demonstrated: by: the following. Aluminumcmelts at temperatures of fromt660? C. to. about 700 C. A sheet of aluminum 0.-1 25 inch thiclcwas-exposed to the tip ofan oxyacetylene frame having-1a temperature of approximately 5500" F: Eiveseconds. were required for this fiametoiburnithroughthe aluminum sheet. When a piece of aluminum having the same. thickness and composition was treated in. accordance withithe method of this invention, by applying a coating. 0.035 inch thick, such coating being hereinafter more particularly described, and againexposed tovthe same acetylene. torch flame, burn.

through i times of. from: 35 to 55 seconds a were. obtained.

Forrcertainxmilitary; purposes, anincrease'inthe time of resistance of: aluminum. of the foregorngthickness of from S tor 35. or 55. seconds. is considerabl y in excess of that which'isneeded-to allow for: expenditure ofsa charge contained insan-aluminum article having a wall thickness. of 0.125 inchs Certain other metals,.althoughi they will not melt at the temperaturesdeveloped by the charge may losetemper; and protection in accordance herewith is valuable. inpreserving such properties for. alonger period of time.

Another requirement of the articles of this invention is thatthey} be able towithstand impact without destroyingylth'e continuity of the coatings Therefore a method' which provides an article having a flexible coating, thereon t is another-object of this invention.

In another adaptation of-thisinvention, articles. which havewheretofore been 1 foneashot items may. be converted to multi-shoti articles since under certain conditions only thecoatingwould: be. destroyed'and'the shell availablerfori recoating, with thecompositions hereof;

It has been foundthatanaqueous coatingcomposition characterizedlb'ythe presence therein of. an aqueous resin cmulsionofi the vinyl or vinylidene. halide type, an alkali metal silicate and: a powdered. siliceous material, is applied'to the surface. of the. metal most nearly in contact with:theheatisource,.allowed to dry,.either by exposure to air or byv force drying, methods, and then exposing the coated. metal: to. temperatures sufl'lcient to soften the metal yields a. resultiwhich is exceedingly beneficial in the rocket propulsion. field:

Broadly stated, therefore,.this invention comprises the provision. of acomposition and method for improving the resistance of metal toutemperatures.suflicient to soften said metal which comprises coatingasaid metal with a liquid coating compositioncontaining as essential ingredients:

(a) from about 10 parts to about 30parts by weightiof having a silica/alkali oxide rat'io of from about 2.6to

about 3.4,"- and? drying, said. coating;

THE AQUEUUS RESIN EMULSION In] general; thezresins which are useful in accordance withi thisdnvention: are in" the" form of an aqueous emulsion'. Not all aqueouscresin emulsions aresuitable for use in: accordance herewith and" to: achieve the best results of this: invention. use? ismade' of" internally plast'i cizedi resins which: are characterized: in that they yield Such resins non=combustibie? decomposition products: include: the: pnlyyinylide'ne: halide polymers and co-poly mere; a'n'dttlre vinyli halide polymers and co-polymers; A

aeoaaov 3 a 1 I preferred class of resins for use in accordance with this invention comprise those having as a base a resin prepared by the polymerization of a monomeric material comprising a haloethylene compound having from 1 to 2 halogen atoms on no more than 1 of the carbon atoms. These may be prepared by dispersing the solid finely divided polymer in water, or by polymerizing the monomeric material in aqueous emulsion. More specifically, the aqueous emulsions may be prepared by polymerizingin aqueous emulsion vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, mixtures of these materials with each other, or mixtures of one or more of these materials with other monomers co-polymerizable therewith in aqueous emulsions such as the vinyl esters of low molecular weigh aliphatic acids such as vinyl acetate, vinyl propionate, vinyl butyrate, and the alkyl esters of acrylic and methacrylic acids such as methyl acrylate, methy methacrylate, ethyl acrylate, ethyl methacrylate, methyl ethacrylate, maleic acid or anhydride esters of maleic acid or of chloro maleic acid, and other similar materials. Particularly preferred are the aqueous emulsions prepared'by polymerization in aqueous emulsion of vinyl chloride, vinylidene chloride, mixtures of these two materials with each other, or mixtures of one or both of these materials with a lesser proportion of an alkyl ester of an alpha-methylene aliphatic mono-carboxylic acid. Examples of the latter are the alkyl esters of acrylic or methacrylic acid or the like. While it is preferred to use the well-known volatile esters of lower alcohols such as methylacrylate, ethylacrylate, methylacrrylate, and the like, other esters of acrylic acid such as butyl acrylate, dodecyl acrylate, phenyl acrylate, ethylene diacrylate, and the like may also be used. A preferred class of resins consists of those made from monomeric materials in which the chloro-ethylene is the predominant constituent, that is, amounts to more than 50% by weight of the material. Complete instructions concerning the preparation of these vinyl resin emulsions may be found in U. S. Patent 2,431,745.

In general, the vinyl resin emulsions contain 40 to 60% solids and are employed in the compositions of this invention in amounts ranging from to 30% by weight of the composition. It is an important criterion of the aqueous emulsion resins that they be stable under fairly strong alkaline conditions. Experience has indicated that polymers and co-polymers of halide-free monomers when the halide-free monomer was in the major amount, are generally unsuited for use in accordance with this invention. Thus, rubber latices, styrene-butadiene latices, and the like are not satisfactory for these purposes.

It has been found that the aqueous emulsion utilized in accordance with this invention impart an impact resistance to the coating composition when applied as a film over the metal. However, there is another distinct advantage of this particular class of emulsion resins and that is to provide under firing conditions a decomposable material, the decomposition products of which are essentially non-combustible which in the presence of the remaining essential ingredients of the composition in the fused state cause intumescence or the production of voids within the fused mass.

THE SILICEOUS COMPONENT The siliceous materials suitable for use in accordance with the present invention are generally of the inactive type. Specific examples of such siliceous materials include Georgia kaolin, china clay, bentonite, diatomaceous silica, perlite, and the like. These materials in combination with the alkali silicate are capable of forming a fusible mass and in further combination with the latex forms an intumesced porous mass serving as an insulating film from the high temperatures. Another function of the siliceous component is to provide a. reinforcing pigment for the silicate which in the absence of the siliceous component would provide an entirely unsatisfactory film due to cracking and spawling. It has also been found that inclusion of the siliceous component in these compositions aids in the release of water when the composition is drying. Thus, it is preferred that the siliceous component employed in these compositions, while easily dispersible in water, should not have too great a water ad'sorptive power. Bentonite, while it may be used, nev-' ertheless produces a less satisfacory product. A preferred example of siliceous material is perlite in the expanded or unexpanded form. This material provides a 4 much faster release of water and may be used as a replacement of part or all of other clay components such as Georgia kaolin or diatomaceous silica. Perlite also aids in producing a composition which is much more suited to spray application. Perlite is a volcanic glass.

In general, the amount of siliceous material employed is from about 15 to 45 parts per parts of composition.

THE ALKALI METAL SILICATE The alkali metal silicate used in accordance with this invention is employed as an aqueous solution containing from 25 to 45% alkali metal silicate. Generally the commercially available sodium silicate having a silica ratio of from 2.5 to about 3.4 and available as approximately 38% solutions may be used. Sodium silicate, potassium silicate or lithium silicate may be employed with sodium silicate being preferred because of its ready availability and low cost. In general from 50 parts to 75 parts per 100 parts of coating composition of the commercial approximately 38% solution is employed. If the viscosity of the resulting composition is too high it has been found convenient to add up to 10% by weight of water to adjust the viscosity to a suitable brushing or spraying consistency.

The foregoing materials may be combined by simple mixing, but it is preferred to pass the composition through a paint mill.

It becomes convenient at this point to illustrate the manner in which compositions suitable for use in accordance herewith may be formulated by giving a few specific, examples which are to be understood as illustrative only and not to be construed as limiting the invention to the precise scope thereof.

Example I 301 lbs. of Georgia kaolin clay were mixed with 55.5 gallons of a sodium silicate solution having a sodium oxide to silicon dioxide ratio of 123.22 and a specific gravity of 41.0% Baum. This mixture was passed rapidly through a roller mill and to the milled mixture were added 29.25 gallons of a polyvinylidene chloride-polyvinyl chloride co-polymer containing a small amount of an alkyl ester of an alpha methylene aliphatic monocarboxylic acid such as methyl methacrylate. This resin emulsion had a solids content of 50% The resulting composition was then ready for use in coating expendable metal objects.

Example [I 326 lbs. of Georgia kaolin clay, 71 lbs. of diatomaceous silica, 50.5 gallons of a potassium silicate solution having a potassium oxide to silicon dioxide ratio of 1:329 and a specific gravity of 40.75 Baum, and 15 gallons of water were mixed together and passed through a roller mill. This composition was then blended with 7 gallons of water and 10 gallons of an aqueous emulsion having a solids content of 50% of a polyvinylidene chloride-polyvinyl chloride co-polymer such as used in Example I above. This composition Was then ready for use in coating expendable metal objects.

Example III 300 lbs. of perlite (volcanic glass), 70 lbs. of Georgia kaolin clay and 51.5 gallons of a sodium silicate solution having a sodium oxide to silicon dioxide ratio of 123.22 and a specific gravity of 410 Baum were mixed and ground for 4 hours in a pebble mill and then blended with 23 gallons of an emulsion having a solids content of, 50%, the resinous component of said aqueous emulsion being a polyvinylidene chloride-polyvinyl chloride resin This composition was then ready for use in accordance with this invention.

Other examples may be formulated in accordance with the instructions illustrated above to provide further compositions which are useful in accordance herewith. The foregoing examples show compositions which contain a vinylidene halide resin emulsion in amounts ranging from about 9.5% or 10% to about 30% by weight of the composition when calculated as a 50% solids solution. The siliceous material as exemplified by kaolin and diatomaceous silica maybe employed in amounts ranging from about 15 to about 45% by weight of the entire compositi on. The alkali metal silicate component in the foregoing examples was anapproximately 38% solution and as such may account for anywhere from 50 to 75% by weight of the entire composition. Mixed siliceous materials may be employed as illustrated in Example II. While sodium silicate is a convenient alkali metal silicate for use in accordance herewith, potassium silicate or lithium silicate solutions may also be employed. Lithium silicate solutions are, however, impractical from a commercial point of view.

The compositions of this invention may be applied conveniently by spray, brush, or dip methods, to provide a film which is preferably from 0.02 to 0.06 inch thick. These films may be air dried, but for best results it has been found that force drying at a temperature not exceeding about 210 F. for a period of 45 minutes to 1 hour is to be desired. If higher tempera tures for drying are employed, certain latices may tend to fuse and form a film over the surface before the water is completely expelled. Too low temperatures for drying do not appear to give satisfactory water release.

The compositions of this invention when dried as films are completely water-soluble. An additional ingredient, such as wax or a silicone resin, may be incorporated in the coating compositions to improve the water resistance of the film. Other methods of insolubilizing alkali silicate films are well known, such as acidtor acid salt treatment. The water sensitive films may also be protected by the use of a lacquer or latex emulsion top coating which may or may not be pigmented, such as for identification purposes.

The annexed drawing is a fragmentary isometric view of an article produced in accordance with this invention, having a base metal 1, such as aluminum, and a film 2 applied thereover and formed from one of the compositions of this invention.

Other modes of applying the principle of this invention may be employed instead of those specifically set forth above, changes being made as regards the details herein disclosed, provided the elements set forth in any of the following claims, or the equivalent of such be employed.

We, therefore, particularly point out and distinctly claim as our invention:

1. The method for improving the resistance of metal to temperatures sufficient to soften said metal which comprises coating said metal with a liquid coating compo sition containing as essential ingredients: (a) from about parts to about 30 parts by weight of an aqueous resin emulsion of 40% to 60% solids concentration; said resin being selected from the group consisting of vinylidene halide polymers and co-polymers and vinyl halide polymers and co-polymers; (b) from about parts to about 45 parts of a powdered siliceous material having a particle size of from about 100 mesh to 400 mesh, and (c) from about 50 parts to about 75 parts of a to 45% aqueous solution of an alkali metal silicate having a silica/alkali oxide ratio of from about 2.6 to about 3.4 and drying said coating.

2. The method for improving the resistance of metal having melting points in the range of from about 500 C. to about 1500 C. to temperatures suflicient to soften said metal which comprises coating said metal with a liquid coating composition containing as essential mgredients: (a) from about 10 parts to about 30 parts by weight of an aqueous resin emulsion of 40% to 60% solids concentration, said resin being selected from the group consisting of vinylidene halide polymers and copolymers and vinyl halide polymers and co-polymers; (b) from about 15 parts to about parts of a powdered siliceous material having a particle size of from about 100 mesh to 400 mesh, and (c) from about parts to about 75 parts of a 20% to 45 aqueous solution of an alkali metal silicate having a silica/alkali oxide ratio of from about 2.6 to about 3.4 and drying said coating.

3. The method of improving the resistance of aluminum to temperatures suificient to soften the aluminum which comprises coating the aluminum with a liquid coat ing composition containing as essential ingredients: (a) from about 10 parts to about 30 parts by weight of an aqueous resin emulsion of 40% to solids concentration; said resin being selected from the group consisting of vinylidene halide polymers and co-polymers and vinyl halide polymers and co-polymers; (b) from about 15 parts to about 45 parts of a powdered siliceous material having a particle size of from about 100 mesh to 400 mesh, and (c) from about 50 parts to about parts of a 20% to 45% aqueous solution of an alkali metal silicate having a silica/alkali oxide ratio of from about 2.6 to about 3.4 and drying said coating.

4. As an article of manufacture aluminum coated with the composition described in claim 1.

5. The method for improving the resistance of magnesium-containing metals to temperatures sulficient to soften said metal which comprises coating said metal with a liquid coating composition containing as essential ingredients: (a) from about 10 parts to about 30 parts by weight of an aqueous resin emulsion of 40% to 60% solids concentration; said resin being selected from the group consisting of vinylidene halide polymers and co-polymers and vinyl halide polymers and co-polymers; (b) from about 15 parts to about 45 parts of a powdered siliceous material having a particle size of from about mesh to 400 mesh, and (c) from about 50 parts to 75 parts of a 20% to 45% aqueous solution of an alkali metal silicate having a silica/alkali oxide ratio of from about 2.6 to about 3.4, and drying said coating.

6. A coating composition for improving the resistance of metal to temperatures sufiicient to soften the metal comprising: (a) from about 10 parts to about 30 parts by weight of an aqueous resin emulsion of 40% to 60% solids concentration; said resin being selected from the group consisting of vinylidene halide polymers and copolymers and vinyl halide polymers and co-polymers; (b) from about 15 parts to about 45 parts of a pow dered siliceous material having a particle size of from about 100 mesh to 400 mesh, and (c) from about 50 parts to about 75 parts of a 20% to 45% aqueous solution of an alkali metal silicate having a silica/alkali oxide ratio of from about 2.6 to about 3.4.

References Cited in the file of this patent UNITED STATES PATENTS 2,597,872 Iler May 27, 1952 

1. THE METHOD FOR IMPROVING THE RESISTANCE OF METAL TO TEMPERATURES SUFFICIENT TO SOFTEN SAID METAL WHICH COMPRISES COATING SAID METAL WITH A LIQUID COATING COMPOSITION CONTAINING AS ESSENTIAL INGREDIENTS: (A) FROM ABOUT 10 PARTS TO ABOUT 30 PARTS BY WEIGHT OF AN AQUEOUS RESIN EMULSION OF 40% TO 60% SOLIDS CONCENTRATION; SAID RESIN BEING SELECTED FROM THE GROUP CONSISTING OF VINYLIDENE HALIDE POLYMERS AND CO-POLYMERS AND VINYL HALIDE POLYMERS AND CO-POLYMERS; (B) FROM ABOUT 15 PARTS TO ABOUT 45 PARTS OF A POWDERED SILICEOUS MATERIAL HAVING A PARTICLE SIZE OF FROM AOBUT 100 MESH TO 400 MESH, AND (C) FROM ABOUT 50 PARTS TO ABOUT 75 PARTS OF A 20% TO 45% AQUEOUS SOLUTION OF AN ALKALI METAL SILICATE HAVING A SILICA/ALKALI OXIDE RATIO OF FROM ABOUT 2.6 TO ABOUT 3.4 AND DRYING SAID COATING.
 6. A COATING COMPOSITION FOR IMPROVING THE RESISTANCE OF METAL TO TEMPERATURES SUFFICIENT TO SOFTEN THE METAL COMPRISING: (A) FROM ABOUT 10 PARTS TO ABOUT 30 PARTS BY WEIGHT OF AN AQUEOUS RESIN EMULSION OF 40% TO 60% SOLIDS CONCENTRATION; SAID RESIN BEING SELECTED FROM THE GROUP CONSISTING OF VINYLIDENE HALIDE POLYMERS AND COPOLYMERS AND VINYL HALIDE POLYMERS AND CO-POLYMERS; (B) FROM ABOUT 15 PARTS TO ABOUT 45 PARTS OF A POWDERED SILICEOUS MATERIAL HAVING A PARTICLE SIZE OF FROM ABOUT 100 MESH TO 400 MESH, AND (C) FROM ABOUT 50 PARTS TO ABOUT 75 PARTS OF A 20% TO 45% AQUEOUS SOLUTION OF AN ALKALI METAL SILICATE HAVING A SILICA/ALKALI OXIDE RATIO OF FROM ABOUT 2.6 TO ABOUT 3.4. 